Spark gap switches are used extensively in high voltage applications in both research and industry, such as in the output stages of high voltage particle accelerators. Such switches normally comprise a pair of electrodes separated by a gap inside a gas filled enclosure. The gas, a common feature of spark gap switches, serves to adjust the characteristics of the switch through its composition and pressure.
High voltage spark gap switches "close" when high voltage between the electrodes causes an arc to be established. This arc breakdown produces very high local temperatures and pressures, with concomitant chemical changes in the surrounding gas. Solid and liquid products of these changes precipitate out onto the interior surfaces of the switch and, if allowed to remain, will adversely affect the characteristics, and shorten the life of the switch through high voltage tracking on switch surfaces. Maintaining these switches in a clean condition over numerous firings is necessary because a typical switch costs approximately $6,500.00, and about two days downtime is required to manually clean or replace a switch.
In order to maintain proper switch performance and prolong the life of the switch over repeated switch operations, it is necessary to effectively clean the contaminating precipitates from the switch surfaces after each firing. Conventional attempts to accomplish this have involved purging the interior of the switch housing with a sweep gas introduced through one port, and withdrawn through a second port. This method is effective in removing contaminates in the switch gas, but is largely ineffective in removing solids or liquids that have precipitated onto switch surfaces.
A somewhat different approach to a contaminate removal system is disclosed in U.S. Pat. No. 4,563,608, to Lawson et al. Here, the switch gas also serves as the sweep gas. The gas is introduced through a nozzle in one of the electrodes, and is circulated through a venturi housing in the other electrode. The patent teaches that the flowing gas serves to control the firing stability of the switch, cool the switch, and carry away the reaction products. However, because of the relatively low gas velocity in the housing after entrainment of the low velocity gas, and the generally nonturbulent flow of this design, it does not appear that precipitated contaminants would be removed effectively from switch surfaces. Additionally, this switch is complex in design, requiring major alteration of the electrode containing the venturi housing and the housing end to which that electrode is mounted.
In U.S. Pat. No. 3,551,737 to Sheets there is disclosed a spark gap where a vortically flowing gas is used to stabilize arc discharge in a tube. The flow is established by four annular holes through which the gas flows into the enclosure. Although a vorticular flow of gas is established, it is not sufficiently turbulent to adequately remove contaminates on the surfaces of the electrodes and associated structures.
It is therefore an object of the present invention to provide a high voltage spark gap switch with improved surface cleaning capability, through use of a turbulent, spirally flowing gas.
It is a further object of the present invention to provide a high voltage spark gap switch having a longer lifetime, and requiring less maintenance than previous spark gap switches.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.